FISH COMMUNITIES AS INDICATORS OF BIOLOGICAL CONDITIONS OF RIVERS: METHODS FOR REFERENCE CONDITIONS

Ambientalia SPI (2011)

FISH COMMUNITIES AS INDICATORS OF BIOLOGICAL CONDITIONS OF

RIVERS: METHODS FOR REFERENCE CONDITIONS

Carlos Alonso, Diego García de Jalón and Miguel Marchamalo

Universidad Politécnica de Madrid

Abstract

Fish communities are a key element in fluvial ecosystems Their position in the top of the food chain and their

sensitivity to a whole range of impacts make them a clear objective for ecosystem conservation and a sound

indicator of biological integrity. The UE Water Framework Directive includes fish community composition,

abundance and structure as relevant elements for the evaluation os biological condition. Several approaches

have been proposed for the evaluation of the condition of fish communities, from the bio-indicator concept

to the IBI (Index of biotic integrity) proposals. However, the complexity of fish communities and their

ecological responses make this evaluation difficult, and we must avoid both oversimplified and extreme

analytical procedures.

In this work we present a new proposal to define reference conditions in fish communities, discussing them

from an ecological viewpoint. This method is a synthetic approach called SYNTHETIC OPEN

METHODOLOGICAL FRAMEWORK (SOMF) that has been applied to the rivers of Navarra.

As a result, it is recommended the integration of all the available information from spatial, modelling,

historical and expert sources, providing the better approach to fish reference conditions, keeping the highest

level of information and meeting the legal requirements of the WFD.

Keywords: fish, WFD, biological integrity, reference conditions, Spain

1. INTRODUCTION

Fish communities are a sensitive part of

fluvial ecosystems, since they are located in the

upper part of the trophic chain and require

different habitats and, sometimes, large

connected areas for the completion of their life

cycle. Thus they also integrate adverse effects of

complex and varied stresses on other components

of the aquatic ecosystem. Furthermore, they are

relatively long-lived so they can reflect

disturbances happened in a longer period than

other taxa can. These mentioned characteristics

and their major societal visibility make fish a useful

element or river ecosystem to measure

environmental degradation (Fausch et al. 1990).

The WFD includes composition,

abundance and age structure of fish fauna as

quality elements to be evaluated in rivers and

lakes. This evaluation requires an effort in

monitoring, as age structure requires dating

individuals and sampling reaches must be large

C. Alonso, D. García de Jalón and M. Marchamalo (2011)

Ambientalia SPI (2011) 2

enough to include potential habitat and reflect

the local and large migrations through fluvial

systems.

The WFD promotes the original, pristine

communities prior to human disturbance as a

template in order to evaluate the ecological status

of rivers and lakes. Thus, their biological

assessment has to be emphasized on knowing

whether all the elements that should be in the

river are in fact there, and how much the present

community differs from the original one or the

one defined as the reference. In this context,

ecological status should be assessed by means of

the measurement of the deviation of actual

conditions from reference conditions.

Reference conditions are usually defined

as the ones corresponding to a high ecological

status of the fluvial system (Directive 2000/60/EC

of the European Parliament and of the Council of

23 October 2000 establishing a framework for

Community action in the field of water policy). A

water body is in high ecological status when there

are no, or only very minor, anthropogenic

alterations to the values of the physico-chemical

and hydromorphological quality elements for the

surface water body type from those normally

associated with that type under undisturbed

conditions. The values of the biological quality

elements for the surface water body reflect those

normally associated with that type under

undisturbed conditions, and show no, or only very

minor, evidence of distortion. Nevertheless, in a

widely used sense they can be considered

“reference conditions for biological integrity’’ or

RC(BI) (Stoddard et al. 2006), and set the

reference for the preservation or restoration of the

ecological condition to a natural objective (U.S.

Clean Water Act, E.U. Water Framework Directive

, Water Reform Framework in Australia).

Moreover, biological reference conditions are, to

some extent, the expression of the integrity of

ecological processes on the elements of the

ecosystem, so we should talk about reference

processes to use a more meaningful term.

Nevertheless, as elements can be at the same

time, affected by, and drivers of processes, the

structure of an ecosystem can be considered as a

valuable indicator of its processes.

Reference conditions are “type-specific”

and must be set for each water body type in a

given classification system. Type-specific biological,

hydromorphological and physicochemical

conditions shall be established representing the

values of the biological, hydromorphological and

physicochemical quality elements for that surface

water body type at high ecological status as

defined in each regulation (Directive 2000/60/EC

of the European Parliament and of the Council of

23 October 2000 establishing a framework for

Community action in the field of water policy).

Anyway, reference conditions may vary in

different approaches, depending on the objective

or purpose of the biological integrity assessment,

from best remaining ecological conditions to best

past conditions, for example. But, as they should

strictly reflect the integrity of ecological processes,

reference conditions shall be those that can be

attained in the presence of the actual natural

stressors.

In this work we present the main

approaches to fix reference conditions for each

Navarra’s river types using fish community’s traits,

discussing them. This method is a synthetic

approach called SYNTHETIC OPEN

METHODOLOGICAL FRAMEWORK (SOMF) that

has been applied to the rivers of Navarra.

After the assessment of these approaches

from an ecological viewpoint, it is recommended

the integration of all the available information

from spatial, modelling, historical and expert



sources, providing the better approach to fish

reference conditions, keeping the highest level of

information and meeting the legal requirements

of the WFD. These ideas are the basis for the

establishing the new synthetical approach for

identifying fish reference conditions: Open

Methodological Framework.

2. ASSESSING FISH FAUNA STATUS

Biological dimension of fluvial ecosystems

integrates all its biological components from

microorganisms (bacteria, fungi, microalgae,

protozoa, rotifer, cladocer, copepodae,) to

macroorganisms: invertebrates, macrophytes, fish,

amphibians, molluscs, birds, riparian vegetation...

Several biological assessment indexes have been

proposed for specific elements, following three

main approaches: a) bioindicator-based indexes;

b) Indexes of Biotic Integrity (IBI) and Similarity

Indexes (CHE 2005). Fausch et al. (1990) adds

species richness, diversity, and evenness as other

main approach to evaluate fish communities as

indicators of environmental degradation, and

includes similarity indexes as a type of multivariate

methods.

2.1. Bioindicator approach

Bioindicator based indexes are based on

taxa whose ecological requirements and

responses to alterations are enough known as to

be employed as indicators of such alterations. (De

Pauw & Hawkes, 1993). Several scientific groups

have pointed out the potential of aquatic

macroinvertebrates as bioindicators (Hellawell,

1986; Rosenberg and Resh, 1993; Merrit y

Cummins, 1996). This has triggered in the last

decades the production of macroinvetebrate-

based indexes, such as BMWP, Biological

Monitoring Working Party (U.K., Armitage et al.,

1983), BBI (Belgium, De Pauw y Vanhooren,

1983), IBGN (France, AFNOR, 1992), usually

based in a score system, assigning the highest

scores to intolerant taxa and lowest scores con

tolerant taxa.

The bioindicator approach is conceptually

simple and requires no complicated theory. Thus,

it has been easily understood by civil engineers

and technical staff in charge of river management

without any ecological or biological knowledge. It

can also be easily applied with semi-quantitative

(relative abundance) or qualitative (presence-

absence) sampling of fish communities. A finer

resolution of stresses can be attained when

habitat, trophic or reproductive guilds are used.

In the other hand, there are few

guidelines for choosing appropriate indicator taxa

or guilds. Besides, reasons other than degradation

(eg. zoogeographic barriers, overharvesting, or

biological interactions) can be the cause of a

species to be absent. There can be also a regional,

seasonal or age-stage related variation in the

sensitivity of indicator taxa. Moreover, a certain

species can express different sensitivities to

different stressors and besides its presence or

absence cannot distinguish degrees of

degradation. Fausch et al. (1990) suggest

developing an index based on changes expected

in fish communities when degradation occurs.

In addition, indices based on indicator

taxa oversimplify the survey results, as they are

generally obtained by adding the ‘weight factor’

associated to each species present in the

community, which is given on subjective

assessments about the species tolerance or

sensitivity to organic pollution. In this situation, a

more precise taxonomic identification of river

fauna and flora than that required by these

indexes (genus or family level) is necessary, and a

comparative study of the present situation in



relation to the reference condition seems to be

demanded, without any previous consideration of

the species as indicators of water quality, neither

of the scoring system of prescribed values of good

and bad conditions, like those reflected in the

traditional biological indicator based indexes

(García de Jalón, D. & M. Gonzalez Tánago, 2005).

2.2. Biotic Integrity approach

Karr et al. (1986) notice that the term

biotic integrity is to some extent abstract and

elusive. Nonetheless the concept can be defined

as the ability of a system to support and maintain

“a balanced, integrated, adaptive community of

organisms having a species composition, diversity,

and functional organization comparable to that of

natural habitat of the region” (Karr and Dudley

1981), thus providing the system with the ability

to withstand or recover from most natural and

anthropogenic perturbations. According to these

authors, the biotic integrity of a system is thus the

best indicator of its potential.

Indexes of Biotic Integrity (IBI) assume that

reference conditions can be estimated through

various interpretations of the range of metric

values currently observed in a region and that

usually for any specific stream type or stream size,

reference condition is represented by the highest

species richness (Stoddard et al., 2006). This kind

of indices is based on the fact that fish

communities respond to human alterations of

aquatic ecosystems in a predictable and

quantifiable manner There has been several

proposals of IBI indexes focused on

macroinvertebrates (AQEM CONSORTIUM 2002),

aquatic and riparian vegetation (Bunn et al., 1999)

and mainly on fish communities (Karr, 1981;

Fausch et al., 1984; Karr et al., 1986; Schmutz

2004).

The use of this kind of indices is more

widely extended in USA that in the EU (CHE

2005), but there are some experiences in using

this concept to assess the ecological status in the

terms of WFD. IBICAT (Sostoa et al. 2004))

represents an adaptation of IBI (Index of Biotic

Integrity) Karr (1981) to Catalonian rivers (NE

Spain), and it is based on a five-type river

classification for which five corresponding indices

were proposed, thus classifying the ecological

status of rivers into 3 categories. The European

Fish Index (EFI) (FAME CONSORTIUM 2004) is

based on a predictive model that derives

reference conditions for individual sites and

quantifies the deviation between predicted and

observed conditions of the fish fauna. This index

employs 10 metrics describing 5 ecological

function groups: trophic structure, reproduction

guilds, physical habitat, migratory behaviour and

general tolerance to disturbance. The EFI was

developed for Western and Northern Europe and

calibrated against a rough estimate of human

pressure status. This index has recently been

extended by EFI+ CONSORTIUM, whose overall

objective is to overcome existing limitations of the

EFI by developing a new, more accurate and pan-

European fish index. Among the limitations of EFI

was its applicability to Mediterranean rivers, since

fish assemblage’s metric responses to perturbation

across Mediterranean areas were consistently

weaker than those found for Central and

Temperate Europe (Pont et al. 2006; Schmutz et al.

2007). Major bottlenecks for the development of a

multimetric index in Mediterranean regions

included i) a typical low species richness per site, ii)

a high degree of endemicity and basin-specific

taxa assemblages; iii) the naturally harsh and

fluctuating, warm climate-dependent, aquatic

environment, and iv) a complex and hardly-

predictable combination of hydrological variability



with human pressures, either present or inherited

throughout centuries of fluvial and landscape

uses. As a result Segurado et al. (2008) extended

the EFI to be used in Mediterranean rivers

assessment studies, although human pressures are

different that those in Central Europe and have

impacts in the EFI with peculiar patterns (Ferreira

et al., 2007).

The advantages of IBIs are that it is a

broadly based ecological index that assesses both

community structure and function at several

trophic levels, providing biologically meaningful

IBI classes. It is also flexible and has been applied

to various ecological regions where stream fish

communities are at least moderately diverse. The

metrics in which IBI is based are sensitive to many

types of degradation. Its scores are reproducible,

and show consistently ranked sites along known

gradients of degradation (Fausch et al. 1990).

The main disadvantages of these indices

are their methodological requirements (i.e.

complete and careful sampling, at least moderate

species richness, background information on fish

communities from a variety of streams). Besides,

subjectiveness is still not avoided when

establishing metric criteria (Fausch et al. 1990).

Most IBIs are multimetric indices based on

the “reference condition approach” (Bailey et al.

1998), that reflect important component of the

fish community such as taxonomic richness,

habitat and trophic, guild composition, or

individual health and abundance (Schmutz 2004).

2.2. Similarity to reference conditions approach

Similarity indexes were proposed by

Hellawell (1986) to be used on stream bio-

monitoring, especially for aquatic organisms, and

more recently Winward (2000) has suggested

their use for monitoring vegetation resources in

riparian areas. Similarity indexes can be very useful

for quantitative comparison of present vs.

reference conditions, by means of identifying key

species and comparing their abundance and

space and time distribution in present conditions

with those considered as “natural”. Similarity

indexes that mathematically fluctuate between

zero and one are interesting and suitable for WFD

evaluation. They can use qualitative data

(presence/absence of species like those used by

Jaccard, Sorensen [1948], etc.), or quantitative

data (relative abundance of species as proposed

by Raabe, or absolute abundance as proposed in

Czekanowski index). Therefore, in order to assess

the status of the community composition,

qualitative similarity index for comparing to

reference composition can be much appropriated,

while assessing abundance status quantitative

similarity index can be used. Also, these similarity

indexes may be used directly as the EQR

‘ecological quality ratio’ for each metric, as the

index value for the reference conditions is always

one (identity), and the value of the index would

be directly the EQR. Furthermore, if there are

different reference sites for the same river type,

the issue of determining thresholds between “very

good” and “good” ecological status may be

undertaken using the minimum value of similarity

between two communities from these reference

sites (García de Jalón, D. & M. Gonzalez Tánago,

2005).

3. APPROACHES TO REFERENCE CONDITIONS IN

FISH COMMUNITIES

REFCOND Guidance Document (Working

Group 2.3 – REFCOND), (Wallin et al. 2003)

defines the method to be used in determination

and validation of reference conditions for every

river type depending on the information available,

and prescribes that in case of not having enough



environmental data from free of impacts and

pressures sampling stations, then the following

methods should be used:

Method I. Spatially based reference

conditions using data from non disturbed

monitoring sites;

Method II. Reference conditions based on

predictive modelling;

Method III. Temporally based reference

conditions using either historical data or

palaeoreconstruction or a combination of both;

Method IV. Expert judgement.

For spatially based type-specific biological

reference conditions, Member States shall develop

a reference network for each surface water body

type. The network shall contain a sufficient

number of sites of high status to provide a

sufficient level of confidence about the values for

the reference conditions, given the variability in

the values of the quality elements corresponding

to high ecological status for that surface water

body type and the modelling techniques which

are to be applied.

Each of the above cited methods presents

advantages and disadvantages as state Bonada et

al. (2002) based on Owen et al. (2001), so we

consider that misuse or waste of existing

information can be committed when opting for

one given method instead of the others. This fact

may be hard to justify when available data are

often scarce and any information may help to

obtain more accurate results. Owen et al. (2001)

propose that a hierarchical decision process

should be established to assist in the selection of

approach used to establish reference conditions.

The same authors state that where undisturbed or

nearly undisturbed conditions prevail then a

validated spatial network is preferred. If degraded

conditions prevail then minimally disturbed

stations and historical data may be used to model

a good stress-ecological response relationship.

They point out that expert judgement should be

used only as a last resort and then accompanied

by an acceptable validation process.

The establishment of fish fauna reference

conditions requires the exploitation of available

data. Owen et al. (2001) found that the methods

more often used to establishing Reference

conditions in rivers are those based on spatial data

(42%) and the rarest is modelling (10%). However,

analyzing only the cases were fish was used;

spatial data methods were not so important (34%)

while modelling (14%) and Historical data (29%)

were more frequent. Spatial based methods are

best option when unimpacted representative sites

of all river types are available, although they are

expensive to initiate. Modelling is site specific, but

requires data, calibration and validation (Owen et

al. 2001; Johnson, 2001). Methods based on

Historical data are often inexpensive to obtain, but

the data quality may be poor or unknown and

their variability restricted. Finally, expert

judgement incorporates present day’s concepts in

a balanced way, but may be affected by bias.

4. THE SYNTHETIC APPROACH: OPEN

METHODOLOGICAL FRAMEWORK (SOMF)

Reference conditions for a fish community

should reflect their natural variability between

regions and within the same region (Fausch et al.

1990). Thus, the benchmark to which the current

conditions of the community have to be

compared can be known, taking into account its

variation through different scales.

One of the conditions that must be met is

that the methodology used is consistent and can

be applied to different regions at different scales

and that results are comparable. One of the



problems arising from the application of the

concept of reference conditions is the ambiguity

shown by the users of the term, as well as the

different methodologies used to its estimation

(Stoddard et al. 2006).

A synthetic approach that involves the

outputs of all the different types of methods into a

single set of results has been recently proposed. It

has been named Synthetic Open Methodological

Framework, SOMF, and it is designed to reflect the

natural variability of reference conditions within a

river type taking into consideration physiographic

or geographic gradients that drive that variability

(Fausch et al. 1990) such as altitude or river width,

among others, (Alonso et al. 2009).

This methodological framework takes

systematically into account the information

independently obtained by the application of

every known method (namely reference-site

approach, predictive modeling, historical

conditions and expert judgment). This approach

pursues two main objectives:

- to keep the different sensitivities of the

methods, keeping all the information obtained

from the most sensitive method in each case (e.g.

in order to detect whether a species must be

present or not in a given water body in reference

conditions), and

- To estimate the soundness of the

reference conditions thus established, quantified

as a function of the number of methods that

predict them (e.g. the presence of a given species

in a given water body).

This methodology was designed in the

form of an open methodological framework in

order to keep the ability of being adapted to any

circumstances, such as the methods to be

considered in order to accomplish different

national or supra-national normative (e.g. U.S.

Clean Water Act, E.U. Water Framework Directive,

Australian Water Reform Framework), the disposal

of data or the different concepts of reference

conditions to be determined and theoretical

criteria to be used (Stoddard et al. 2006). The

name Synthetic Open Methodological Framework

means that its process of application has not to be

understood as a fixed methodology but as a

highly adaptive logical framework in which only

the fundamentals of the methodology have to be

strictly accomplished, and the specific

circumstances of the case in which it is to be

applied may impose modifications of the details of

the methodology. The fundamentals of SOMF are:

(1) to use of a set of a priori defined

quality elements to accomplish a previously

designed monitoring process (e.g. WFD);

(2) to keep all the available

information after the application of all considered

methods thus taking into consideration the

different sensitiveness of the methods; and

(3) To quantify the soundness of the

results as a function (e.g. linear combination) of

the number of independent methods that lead to

a given reference condition.

For each river type, specific reference

conditions can be determined by means of a two-

phase process:

Phase 1: River type-specific reference

conditions are set for every quality element by

independently using as many different methods

as can be considered; which in our case study are

the four methods given by Guidance Document

no. 10 (Working Group 2.3 – REFCOND) (Wallin

et al. 2003). Within a given river type, reference

conditions can change following a gradient which

might be determined by a physiographic or

geographic variable such as river width, latitude,

altitude,…., or a combination of several of them.



Thus reference conditions should reflect to some

extent this observed gradients.

Figure 1.- Synthesis of several (four) reference

conditions methods into a single integrated result

graph; different shading degrees represent different

degrees of soundness of the results.

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 00 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 00 0 0 1 1 1 1 1 1 1 1 1 1 0 0 0 0 00 0 0 1 1 1 1 2 2 2 2 2 2 1 1 1 1 00 0 0 1 1 1 1 2 2 2 2 2 2 1 1 1 1 00 1 1 2 2 2 2 3 3 3 3 2 2 1 1 1 1 00 1 1 2 2 2 2 3 3 3 3 2 2 1 1 1 1 00 1 1 2 2 2 3 4 4 4 4 3 3 2 2 2 1 00 1 1 2 2 2 3 4 4 4 4 3 3 2 2 2 1 00 1 1 2 2 2 3 4 4 4 4 3 3 2 2 2 1 00 1 1 2 2 2 3 4 4 4 4 3 3 2 2 2 1 00 1 1 1 1 1 2 3 3 3 3 2 2 2 2 2 1 00 1 1 1 1 1 2 3 3 3 3 2 2 2 2 2 1 00 1 1 1 1 1 2 2 2 2 2 1 1 1 1 1 0 00 1 1 1 1 1 2 2 2 2 2 1 1 1 1 1 0 00 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 00 0 0 0 0 0 1 1 1 1 1 1 1 1 1 1 0 00 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

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Quality element component

Method I

Method II

Method III

Method IV

Relaxedreference conditions

Mediumreference conditions

Strictreference conditions

Phase 2: All the information given by each

method is integrated into a synthetic set of

reference conditions accounting for the number

of methods that estimate a certain reference

condition (i.e. the value of every quality element in

theoretical minimally disturbed conditions

according to every method), in a process that can

also hold different weighting coefficients for each

method- although in our case study methods

were weighted equally. This way, robustness of

the estimation can be classified into several

strictness classes (Figure 1): from relaxed (e.g. a

species is only to be in the fish community when

more than 3 methods predict its presence in

reference conditions; the abundance of a given

species is the average of the 3 lowest results of the

4 methods) to strict reference conditions (e.g. a

species is to be in the fish community when as

soon as a single method predicts its presence; the

abundance of a species is the value of the highest

result of the 4 methods).

4.1. Application to Navarra rivers

This synthetic approach was applied

within the context of a project (Gobierno Navarra

2006) funded by Navarra Regional Government

whose main goals were: (1) to classify the rivers of

Navarra, by using preferably “System B” methods;

(2) to set reference conditions for every identified

river type; and (3) to assess the ecological status of

rivers in Navarre according to WFD requirements.

In this paper we deal only with the second goal of

setting the reference conditions of the fish

biological element. These fish reference conditions

were defined for each of the eleven river types

defined for Navarra previously (Gonzalez Tánago

et al, 2006)

Fish communities records from 293

sampling sites among the rivers of Navarra

including composition and species abundances

were used.

In the mentioned project, due to the

geographical characteristics of the river network

of Navarra (narrow latitude and river width

range), altitude was the main gradient variable

with sufficient ecological significance. According

to WFD REFCOND Guidance Document (Wallin et

al. 2003), four methods were used in Phase 1 of

the SOMF application:

- Method I. Spatially based reference

conditions. 32 non- or minimally disturbed sites

were used in the reference-site approach.

- Method II. Predictive models. For each

river type four models were used predicting the

variation of the several variables following a

physiographic gradient (i.e. altitude) in

theoretically undisturbed conditions. Modeled

variables were: (1) proportion of every group of



species (i.e. species that usually coexist) within the

fish community; (2) number of native species in

the fish community; (3) probability of every

species of being present in the fish community;

and (4) relative abundances of every species.

- Method III. Historical or paleo-

reconstruction originated information. Municipal

recordings of Geographic and Statistic Dictionary

of Spain (Madoz 1850) were used as dataset.

- Method IV. Expert judgment.

Results of the application of SOMF

showed the reference conditions for quality

elements composition and relative abundance of

fish community. As an example of the results,

Figure 2 shows the composition of the fish

community in the reference conditions inferred

trough SOMF approach. The different strictness

classes can be noticed by different gray shadings

(the darker shading the stricter reference

conditions).

This synthetic approach was also used to

estimate reference conditions for macro-

invertebrate and microalgae quality elements in

the same project.

The main advantages of the SOMF are its

simplicity, adaptive approach and that it takes

advantage of the different sensitivities of all

considered types of methods. Besides, the

soundness of the reference conditions thus

established can be quantified. It is open, which

means that it can be adapted to strictly fulfill any

theoretical concept or previously designed

methodological process such as national or supra-

national normative.

Furthermore, it allows the use of Similarity

Index based EQRs when assessing the status of

the quality element, quantified in terms of its

deviation from reference condition, thus allowing

knowing to what extent every quality element is

responsible of the observed EQR, and therefore

becoming useful guidelines to set the restoration

goals to be attained in order to reach the good

ecological status.

Figure 2.- Example of the results: species

composition of the fish community in reference

conditions obtained from the application of SOMF

in type 4 rivers (i.e. calcareous medium and small

sized streams of wet mountain climate) of Navarra

1100 0 2 0 0 0 0 0 0 0(...) 0 2 0 0 0 0 0 0 0

650 0 2 0 0 0 0 0 0 0640 1 3 0 0 0 1 1 0 1630 1 3 1 0 0 1 1 0 1620 1 4 1 0 0 2 1 0 1610 1 4 1 0 1 2 1 0 1600 1 4 1 0 1 2 1 0 1590 1 4 2 1 1 3 1 0 3580 1 4 2 1 1 3 1 0 3570 1 4 2 1 1 3 1 0 3560 1 4 2 1 1 3 1 0 3550 1 4 2 1 1 3 1 0 3540 1 4 2 1 1 3 1 0 3530 1 4 2 1 2 3 2 0 3520 1 4 2 1 2 3 2 0 3510 1 4 2 1 2 3 2 0 3500 1 4 1 1 2 3 2 0 3490 2 4 0 1 3 3 3 1 3480 2 4 0 1 3 3 3 1 3470 2 4 0 1 3 3 3 1 3460 2 4 0 1 3 3 3 1 3450 2 4 0 1 3 3 3 1 3440 2 4 0 1 3 3 3 0 3430 2 4 0 1 3 3 3 0 3420 3 4 0 1 4 3 4 0 3410 3 4 0 1 4 3 4 0 3400 3 3 0 1 4 3 4 0 3

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Quality element component: Species

In order to avoid the weaknesses

identified in these kinds of multivariate methods

(namely result interpretation) (Fausch et al. 1990)

more research on causality of identified relations

among impacts and quality elements is needed.

The shift from reference conditions to reference

processes appears to be a major perspective in



river ecological assessment (Dufour and Piégay

2009), and this can be achieved by using SOMF

synthetic approach but much research has to be

done in this direction.

5. CONCLUSIONS

The purpose of this text is to sum up the

different techniques that use fish communities as

indicators of ecological status of rivers,

emphasizing the different methods leading to the

determination of the reference conditions. Misuse

or waste of existing information can be committed

when opting for one given method instead of the

others. This fact may be hard to justify when

available data are often scarce and any

information may help to obtain more accurate

results.

SOMF is not expected to be a revision of

the method establish by WFD to set reference

conditions, but an efficient solution when

reference sites are scarce or not representative of

the whole population of reaches in a given

ecotype

Therefore, SOMF represents a flexible

approach to be used in (riverine) ecosystem

management plans with a flexible framework

designed to envelope a variety of data sets,

methods and ecological concepts, providing

water-resource managers and biologists a tool to

address the question: what should rivers look

like?.

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Acknowledgements

Javier Castiella (Government of Chartered

Community of Navarre), Mariano Cebrián

(Infraestructura y Ecología), María Antonia Valero

(IBERINSA), and staff from HIDROBIOLOGÍA

Research Group (Polytechnic University of

Madrid).

Documents

FISH COMMUNITIES AS INDICATORS OF BIOLOGICAL CONDITIONS OF RIVERS: METHODS FOR REFERENCE CONDITIONS